1. Field of the Invention
The present invention relates in general to a cylindrical door lock and, more particularly, to an improved structure of such a cylindrical door lock for adjusting the backset of the lock in order to be commonly used in both 60 mm backset door and 70 mm backset door.
2. Description of the Prior Art
As well known to those skilled in the art, conventional cylindrical door locks are generally classified into two types, that is, 60 mm backset door locks and 70 mm backset door locks, in accordance with their backsets. Here, the term "backset" means the horizontal distance from the face of a latch bolt to a knob center or a keyhole of a cylindrical door lock. In order to correspond to the commercialized door locks having the above different backsets, the doors which are to be equipped with the door locks should have the different distances from their free edges to the centers of their cylinder knob receiving holes. In this regard, a door should be equipped with a specified cylindrical door lock having a corresponding backset. Otherwise stated, a door of which the distance from its free edge to the center of its knob receiving hole corresponds to the 60 mm backset should be equipped with a 60 mm backset door lock while a door of which the distance from its free edge to the center of its knob receiving hole corresponds to the 70 mm backset should be equipped with a 70 mm backset door lock.
Since the conventional cylindrical door locks are separately produced and commercialized in the 60 mm backset type locks and 70 mm backset type locks, the conventional door locks have a problem in that they, while giving no problem to those skilled in the art, often cause confusion of users who want to change themselves their door locks but have no information about the backsets of the door locks to be changed.
That is, a user who wants to change himself his door lock but has no information about the backset of his door lock will certainly buy a new door lock without confirmation of the backset of the door lock dead bolt. When the backset of the new door lock fortunately fits the door, there will be no problem in installation of the door lock in the door. However, when the backset of the new door lock does not fit the door, the user should call on the lock seller in order to exchange the door lock. This makes the user confused and troubled.